1. Field of the Invention
The invention relates to a flat panel display (FPD), and in particular to an organic electro-luminescent device with prolonged lifetime.
2. Description of the Related Art
Organic electro-luminescent devices or organic light-emitting diodes (OLEDs) are active lighting devices using organic materials. Compared with conventional inorganic LEDs, OLEDs can be easily fabricated on a large substrate by forming an amorphous silicon layer thereon. Additionally, displays utilizing OLEDs require no backlight module, whereby the manufacturing process is simpler and costs are reduced. OLED technology is highly developed and can be employed in small panels such as those in personal digital assistants (PDAs) or digital cameras.
The organic electro-luminescent device typically comprises an anode, a cathode, and an organic light emissive layer disposed therebetween. The organic light emissive layer may comprise a hole transport layer (HTL) adjacent to the anode, an electron transport layer (ETL) adjacent to the cathode and an electro-luminescent layer interposed therebetween. When an electrical potential difference is applied between the anode and the cathode, electrons are injected into the electron transport layer from the cathode and pass through the electron transport layer and the electro-luminescent layer. At the same time, holes are injected into the hole transport layer from the anode and pass therethrough. The injected electrons and holes are recombined at the interface of the electro-luminescent layer and the hole transport layer, releasing energy as light.
Generally, organic electro-luminescent devices are applied in electronic products with a single-sided display. With the progress of electronic products, however, double-sided display has become required for many products, such as collapsible mobile phones. FIG. 3 is a plane view of a conventional double-sided organic electro-luminescent device. The organic electro-luminescent device 10 includes a substrate 11 having two adjacent pixel regions 12 and 14. A bottom-emitting OLED 16 and a thin film transistor 20 are disposed in the pixel region 12. A top-emitting OLED 18 and another thin film transistor 22 are disposed in another pixel region 14. The thin film transistor 20 is electrically connected to the OLED 16 and the thin film transistor 22 is electrically connected to the OLED 18.
However, in order to provide double-sided light emission, a single pixel region in the organic electro-luminescent device 10 must be divided into two pixel regions 12 and 14, thus the aperture ratio (AR) of the device 10 is reduced and in particular to the pixel region 12 that includes the bottom-emitting OLED 16. In order to maintain brightness of the organic electro-luminescent device 10, power consumption must be increased, thus reducing lifetime.